Hard disk drives are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model was established approximately 40 years ago and resembles a phonograph. That is, the hard drive model includes a storage disk or hard disk that spins at a standard rotational speed. An actuator arm or slider is utilized to reach out over the disk. The arm has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The complete assembly, e.g., the arm and head, is called a head gimbal assembly (HGA). Upon the completion of the HGA the next step is the process is the completion of the head stack assembly (HSA) in which the carriage is integrated with the HGA. The HAS is then merged with the disks. Finally, the entire device is packaged for use as a hard disk drive (HDD) assembly.
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are channels or tracks evenly spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.
Over the year's refinement of the disk and the head have provided great reductions in the size of the hard disk drive. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches (micro drives are significantly smaller than that). Refinements also include the use of smaller components and laser advances within the head portion. That is, by reducing the read/write tolerances of the head portion, the tracks on the disk can be reduced in size by the same margin. Thus, as modern laser and other micro recognition technology are applied to the head, the track size on the disk can be further compressed.
However, the decreased track spacing and the overall reduction in component size and weight has resulted in problems with respect to the interaction of the disk (or disks) and the carriage arm(s) (e.g., the suspension and head attached thereto). For example, since the head portion, attached via the suspension to the carriage arm, is located so close to the disk, any faults with respect to the carriage arm (e.g., thickness, pitch or roll) can cause detrimental errors to the head portion including unstable flight and/or loss of alignment with the track it is reading from or writing to.
One solution to the problem of the carriage arm alignment is to measure the carriage arm using a two-datum line method. However, a two-datum line method will not correctly identify roll or pitch versus thickness, in order to resolve the two-datum line discrepancy, a second visual method must be used to differentiate the roll versus pitch versus thickness issues.
However, the limited capabilities of visual reference devices (e.g., an eyeball, camera, etc.) are based on line of sight, limit the best tolerance of the carriage arm to the tolerance limitations of the visual system. In addition, due to the reduced size of present hard disk drive components and further reduction goals of the hard disk drive and components, visual reference evaluation is quickly reaching its maximum limitations.